Effects of Lithium Halides on Electrode–Electrolyte Bifunctional Materials for High-Capacity All-Solid-State Batteries

All-solid-state batteries have attracted attention because of their high energy density, safety, and long cycle life. Sulfide active materials exhibit high capacities and enable an enhanced energy density in all-solid-state batteries. In this study, we synthesized electrode–electrolyte bifunctional materials in the system Li2S–V2S3–LiX (X = F, Cl, Br, or I) through a mechanochemical process. In addition, the effects of the addition of lithium halides on the electrochemical properties were investigated. All-solid-state batteries with the Li2S–V2S3–LiI electrode showed the highest capacity of 400 mAh g–1 among all the cells, even though their electronic and ionic conductivities were the same. From the point of view of the ionic conductivity and structure of the electrodes during cycling, it was clarified that a high reversible capacity was achieved not only by high ionic and electronic conductivities before cycling but also by maintaining the ionic conductivity even at the deep state of charge. Furthermore, high-loading all-solid-state cells were fabricated using the Li2S–V2S3–LiI materials with a mass loading of 37.3 mg cm–2, exhibiting a high areal capacity of approximately 11.5 mAh cm–2 at 60 °C and good cycle performance.